Hello! Came here from Reddit. How can I "follow"/"join" this "sub" like there

You can follow the sub just like you would on Reddit. The exact placement of things may vary depending on which client/app you use, if on mobile, but there should be an option to subscribe somewhere on the community page or in the menu of one of the posts from here.

You will then find your home or local feed where only what you follow will appear.